I
N
ROA (Relay Operate Angle)
ROA = 60 deg
REFPDIF never operates for any faults
external to the protected zone.
Currents 3I
o
and I
N
are theoretically
180
o
out of phase for any external
ground-fault.
ANSI05000724 V3 EN-US
Figure 64: Zero sequence currents at an external ground fault
ANSI05000725 V3 EN-US
Figure 65: Zero sequence currents at an internal ground fault
1. For an external ground fault (Figure 64), the residual current 3I
o
and the neutral current I
N
have equal magnitude, but they are seen within the IED as 180 degrees out-of-phase if the
current transformers are connected as in Figure
64, which is the ABB recommended
Section 6 1MRK 502 066-UUS B
Differential protection
170
Technical manual
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